Various types of test apparatus are known to check the functioning and operability of electrical apparatus in automotive vehicles, as well as of other apparatus which can be coupled to transducers providing electrical signals. Such test apparatus may, for example, check the proper operation of ignition control systems by determining the appropriate timing of current flow through an ignition coil, interruption of the current flow to determine spark advance or spark timing and the like; or, for example, to check the operation and timing of fuel injection systems, as well as the associated electronic control systems and apparatus. Other types of test apparatus permit checking the illumination system of an automotive vehicle, the voltage regulator of the generator or, for example, the control, operability, and performance of a brake anti-block system.
Testing electrical apparatus, or other apparatus coupled to a transducer, by use of test apparatus is well known. Coupling between the test apparatus and the transducers or a test socket is usually done by connecting a plurality of cables with the vehicle, interconnecting the respective transducers or electrical systems with a stationary test apparatus, remote from the vehicle,and, for example, forming the property of and installed in a service station or repair shop. German Patent Disclosure Document DE-OS 34 10 752 discloses a way to reduce the number of cables between the vehicle and the test apparatus by processing the measured signals to be transduced, for example by converting the signals into digital signals so that they can then be transmitted over a single cable to the test apparatus. This arrangement substantially reduces the number of wires and cables which must be used to connect the vehicle to the test apparatus; yet, the vehicle and the test apparatus must be located in relatively close vicinity, and the vehicle must be coupled to the test apparatus by this "umbilical cord"; the vehicle and the test apparatus, thus, cannot be located at random positions and, further, the vehicle cannot be operated, for example driven, over any but the most restricted distance without severing the test connections between the vehicle and the test or diagnostic apparatus.